Oh! Sorry, then I misunderstood you.
Unfortunately, I probably still have bad news. I don’t have the app myself, so I can only go on what I find online - and the official manual for the app only mentions the possibility of loading plans that have previously been saved by the simulator:
After creating a flight plan, you can save it to load later by pressing the Menu button while in the active flight plan screen. You can also reverse the order of waypoints or delete the entire plan from this menu. To load a saved plan, use the small knob to go to the second screen of the Flight Plan category. Any .fms file that has been saved in the app can be selected from this list.
X-Plane Mobile Manual | X-Plane
It does hint about a .fms file, which is what’s used in the desktop version of the simulator to load flightplans from files, but to my knowledge, there is no way to access such files in iPadOS without a jailbreak. The manual does not mention anything of the sort, and I can’t find anything else online that suggests that it is possible to load external files.
Sorry about this inconvenience!
Kind Regards,
Malte